/*
 * $Id: CalendarUtils.java 3916 2011-01-12 10:21:58Z kleopatra $
 *
 * Copyright 2007 Sun Microsystems, Inc., 4150 Network Circle,
 * Santa Clara, California 95054, U.S.A. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
package org.jdesktop.swingx.calendar;

import java.util.Calendar;
import java.util.Date;

/**
 * Calendar manipulation.
 * 
 * PENDING: replace by something tested - as is c&p'ed dateUtils to work on a
 * calendar instead of using long
 * 
 * @author Jeanette Winzenburg
 */
public class CalendarUtils {

	// Constants used internally; unit is milliseconds
	@SuppressWarnings("unused")
	public static final int ONE_MINUTE = 60 * 1000;
	@SuppressWarnings("unused")
	public static final int ONE_HOUR = 60 * ONE_MINUTE;
	@SuppressWarnings("unused")
	public static final int THREE_HOURS = 3 * ONE_HOUR;
	@SuppressWarnings("unused")
	public static final int ONE_DAY = 24 * ONE_HOUR;

	public static final int DECADE = 5467;
	public static final int YEAR_IN_DECADE = DECADE + 1;

	/**
	 * Increments the calendar field of the given calendar by amount.
	 * 
	 * @param calendar
	 * @param field
	 *            the field to increment, allowed are all fields known to
	 *            Calendar plus DECADE.
	 * @param amount
	 * 
	 * @throws IllegalArgumentException
	 */
	public static void add(Calendar calendar, int field, int amount) {
		if (isNativeField(field)) {
			calendar.add(field, amount);
		} else {
			switch (field) {
				case DECADE:
					calendar.add(Calendar.YEAR, amount * 10);
					break;
				default:
					throw new IllegalArgumentException("unsupported field: " + field);
			}

		}
	}

	/**
	 * Gets the calendar field of the given calendar by amount.
	 * 
	 * @param calendar
	 * @param field
	 *            the field to get, allowed are all fields known to Calendar
	 *            plus DECADE.
	 * 
	 * @throws IllegalArgumentException
	 */
	public static int get(Calendar calendar, int field) {
		if (isNativeField(field)) {
			return calendar.get(field);
		}
		switch (field) {
			case DECADE:
				return decade(calendar.get(Calendar.YEAR));
			case YEAR_IN_DECADE:
				return calendar.get(Calendar.YEAR) % 10;
			default:
				throw new IllegalArgumentException("unsupported field: " + field);
		}
	}

	/**
	 * Sets the calendar field of the given calendar by amount.
	 * <p>
	 * 
	 * NOTE: the custom field implementations are very naive (JSR-310 will do
	 * better) - for decade: value must be positive, value must be a multiple of
	 * 10 and is interpreted as the first-year-of-the-decade - for
	 * year-in-decade: value is added/substracted to/from the start-of-decade of
	 * the date of the given calendar
	 * 
	 * @param calendar
	 * @param field
	 *            the field to increment, allowed are all fields known to
	 *            Calendar plus DECADE.
	 * @param value
	 *            the decade to set, must be a
	 * 
	 * @throws IllegalArgumentException
	 *             if the field is unsupported or the value is not dividable by
	 *             10 or negative.
	 */
	public static void set(Calendar calendar, int field, int value) {
		if (isNativeField(field)) {
			calendar.set(field, value);
		} else {
			switch (field) {
				case DECADE:
					if (value <= 0) {
						throw new IllegalArgumentException("value must be a positive but was: " + value);
					}
					if (value % 10 != 0) {
						throw new IllegalArgumentException("value must be a multiple of 10 but was: " + value);
					}
					int yearInDecade = get(calendar, YEAR_IN_DECADE);
					calendar.set(Calendar.YEAR, value + yearInDecade);
					break;
				case YEAR_IN_DECADE:
					int decade = get(calendar, DECADE);
					calendar.set(Calendar.YEAR, value + decade);
					break;
				default:
					throw new IllegalArgumentException("unsupported field: " + field);
			}

		}
	}

	/**
	 * @param calendarField
	 * @return
	 */
	private static boolean isNativeField(int calendarField) {
		return calendarField < DECADE;
	}

	/**
	 * Adjusts the Calendar to the end of the day of the last day in DST in the
	 * current year or unchanged if not using DST. Returns the calendar's date
	 * or null, if not using DST.
	 * <p>
	 * 
	 * 
	 * @param calendar
	 *            the calendar to adjust
	 * @return the end of day of the last day in DST, or null if not using DST.
	 */
	public static Date getEndOfDST(Calendar calendar) {
		if (!calendar.getTimeZone().useDaylightTime())
			return null;
		long old = calendar.getTimeInMillis();
		calendar.set(Calendar.MONTH, Calendar.DECEMBER);
		endOfMonth(calendar);
		startOfDay(calendar);
		for (int i = 0; i < 366; i++) {
			calendar.add(Calendar.DATE, -1);
			if (calendar.getTimeZone().inDaylightTime(calendar.getTime())) {
				endOfDay(calendar);
				return calendar.getTime();
			}
		}
		calendar.setTimeInMillis(old);
		return null;
	}

	/**
	 * Adjusts the Calendar to the end of the day of the first day in DST in the
	 * current year or unchanged if not using DST. Returns the calendar's date
	 * or null, if not using DST.
	 * <p>
	 * 
	 * Note: the start of the day of the first day in DST is ill-defined!
	 * 
	 * @param calendar
	 *            the calendar to adjust
	 * @return the start of day of the first day in DST, or null if not using
	 *         DST.
	 */
	public static Date getStartOfDST(Calendar calendar) {
		if (!calendar.getTimeZone().useDaylightTime())
			return null;
		long old = calendar.getTimeInMillis();
		calendar.set(Calendar.MONTH, Calendar.JANUARY);
		startOfMonth(calendar);
		endOfDay(calendar);
		for (int i = 0; i < 366; i++) {
			calendar.add(Calendar.DATE, 1);
			if (calendar.getTimeZone().inDaylightTime(calendar.getTime())) {
				endOfDay(calendar);
				return calendar.getTime();
			}
		}
		calendar.setTimeInMillis(old);
		return null;
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the start
	 * of a day (in the calendar's time zone). The calendar is unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the start of the day, false
	 *         otherwise.
	 */
	public static boolean isStartOfDay(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, -1);
		return temp.get(Calendar.DATE) != calendar.get(Calendar.DATE);
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the end of
	 * a day (in the calendar's time zone). The calendar is unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the end of the day, false
	 *         otherwise.
	 */
	public static boolean isEndOfDay(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, 1);
		return temp.get(Calendar.DATE) != calendar.get(Calendar.DATE);
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the start
	 * of a month (in the calendar's time zone). Returns true, if the time is
	 * the start of the first day of the month, false otherwise. The calendar is
	 * unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the start of the first day of the
	 *         month, false otherwise.
	 */
	public static boolean isStartOfMonth(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, -1);
		return temp.get(Calendar.MONTH) != calendar.get(Calendar.MONTH);
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the end of
	 * a month (in the calendar's time zone). Returns true, if the time is the
	 * end of the last day of the month, false otherwise. The calendar is
	 * unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the end of the last day of the
	 *         month, false otherwise.
	 */
	public static boolean isEndOfMonth(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, 1);
		return temp.get(Calendar.MONTH) != calendar.get(Calendar.MONTH);
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the start
	 * of a month (in the calendar's time zone). Returns true, if the time is
	 * the start of the first day of the month, false otherwise. The calendar is
	 * unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the start of the first day of the
	 *         month, false otherwise.
	 */
	public static boolean isStartOfWeek(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, -1);
		return temp.get(Calendar.WEEK_OF_YEAR) != calendar.get(Calendar.WEEK_OF_YEAR);
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the end of
	 * a week (in the calendar's time zone). Returns true, if the time is the
	 * end of the last day of the week, false otherwise. The calendar is
	 * unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the end of the last day of the
	 *         week, false otherwise.
	 */
	public static boolean isEndOfWeek(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, 1);
		return temp.get(Calendar.WEEK_OF_YEAR) != calendar.get(Calendar.WEEK_OF_YEAR);
	}

	/**
	 * Adjusts the calendar to the start of the current week. That is, first day
	 * of the week with all time fields cleared.
	 * 
	 * @param calendar
	 *            the calendar to adjust.
	 * @return the Date the calendar is set to
	 */
	public static void startOfWeek(Calendar calendar) {
		calendar.set(Calendar.DAY_OF_WEEK, calendar.getFirstDayOfWeek());
		startOfDay(calendar);
	}

	/**
	 * Adjusts the calendar to the end of the current week. That is, last day of
	 * the week with all time fields at max.
	 * 
	 * @param calendar
	 *            the calendar to adjust.
	 */
	public static void endOfWeek(Calendar calendar) {
		startOfWeek(calendar);
		calendar.add(Calendar.DATE, 7);
		calendar.add(Calendar.MILLISECOND, -1);
	}

	/**
	 * Adjusts the calendar to the end of the current week. That is, last day of
	 * the week with all time fields at max. The Date of the adjusted Calendar
	 * is returned.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 * @param date
	 *            the Date to use.
	 * @return the end of the week of the given date
	 */
	public static Date endOfWeek(Calendar calendar, Date date) {
		calendar.setTime(date);
		endOfWeek(calendar);
		return calendar.getTime();
	}

	/**
	 * Adjusts the calendar to the start of the current week. That is, last day
	 * of the week with all time fields at max. The Date of the adjusted
	 * Calendar is returned.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 * @param date
	 *            the Date to use.
	 * @return the start of the week of the given date
	 */
	public static Date startOfWeek(Calendar calendar, Date date) {
		calendar.setTime(date);
		startOfWeek(calendar);
		return calendar.getTime();
	}

	/**
	 * Adjusts the given Calendar to the start of the decade.
	 * 
	 * @param calendar
	 *            the calendar to adjust.
	 */
	public static void startOfDecade(Calendar calendar) {
		calendar.set(Calendar.YEAR, decade(calendar.get(Calendar.YEAR)));
		startOfYear(calendar);
	}

	/**
	 * @param year
	 * @return
	 */
	private static int decade(int year) {
		return (year / 10) * 10;
	}

	/**
	 * Adjusts the given Calendar to the start of the decade as defined by the
	 * given date. Returns the calendar's Date.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 * @param date
	 *            the Date to use.
	 * @return the start of the decade of the given date
	 */
	public static Date startOfDecade(Calendar calendar, Date date) {
		calendar.setTime(date);
		startOfDecade(calendar);
		return calendar.getTime();
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the start
	 * of a decade (in the calendar's time zone). Returns true, if the time is
	 * the start of the first day of the decade, false otherwise. The calendar
	 * is unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the start of the first day of the
	 *         month, false otherwise.
	 */
	public static boolean isStartOfDecade(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, -1);
		return decade(temp.get(Calendar.YEAR)) != decade(calendar.get(Calendar.YEAR));
	}

	/**
	 * Adjusts the given Calendar to the start of the year.
	 * 
	 * @param calendar
	 *            the calendar to adjust.
	 */
	public static void startOfYear(Calendar calendar) {
		calendar.set(Calendar.MONTH, Calendar.JANUARY);
		startOfMonth(calendar);
	}

	/**
	 * Adjusts the given Calendar to the start of the year as defined by the
	 * given date. Returns the calendar's Date.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 * @param date
	 *            the Date to use.
	 * @return the start of the year of the given date
	 */
	public static Date startOfYear(Calendar calendar, Date date) {
		calendar.setTime(date);
		startOfYear(calendar);
		return calendar.getTime();
	}

	/**
	 * Returns a boolean indicating if the given calendar represents the start
	 * of a year (in the calendar's time zone). Returns true, if the time is the
	 * start of the first day of the year, false otherwise. The calendar is
	 * unchanged.
	 * 
	 * @param calendar
	 *            the calendar to check.
	 * 
	 * @return true if the calendar's time is the start of the first day of the
	 *         month, false otherwise.
	 */
	public static boolean isStartOfYear(Calendar calendar) {
		Calendar temp = (Calendar) calendar.clone();
		temp.add(Calendar.MILLISECOND, -1);
		return temp.get(Calendar.YEAR) != calendar.get(Calendar.YEAR);
	}

	/**
	 * Adjusts the calendar to the start of the current month. That is, first
	 * day of the month with all time fields cleared.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 */
	public static void startOfMonth(Calendar calendar) {
		calendar.set(Calendar.DAY_OF_MONTH, 1);
		startOfDay(calendar);
	}

	/**
	 * Adjusts the calendar to the end of the current month. That is the last
	 * day of the month with all time-fields at max.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 */
	public static void endOfMonth(Calendar calendar) {
		// start of next month
		calendar.add(Calendar.MONTH, 1);
		startOfMonth(calendar);
		// one millisecond back
		calendar.add(Calendar.MILLISECOND, -1);
	}

	/**
	 * Adjust the given calendar to the first millisecond of the given date.
	 * that is all time fields cleared. The Date of the adjusted Calendar is
	 * returned.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 * @param date
	 *            the Date to use.
	 * @return the start of the day of the given date
	 */
	public static Date startOfDay(Calendar calendar, Date date) {
		calendar.setTime(date);
		startOfDay(calendar);
		return calendar.getTime();
	}

	/**
	 * Adjust the given calendar to the last millisecond of the given date. that
	 * is all time fields cleared. The Date of the adjusted Calendar is
	 * returned.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 * @param date
	 *            the Date to use.
	 * @return the end of the day of the given date
	 */
	public static Date endOfDay(Calendar calendar, Date date) {
		calendar.setTime(date);
		endOfDay(calendar);
		return calendar.getTime();
	}

	/**
	 * Adjust the given calendar to the first millisecond of the current day.
	 * that is all time fields cleared.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 */
	public static void startOfDay(Calendar calendar) {
		calendar.set(Calendar.HOUR_OF_DAY, 0);
		calendar.set(Calendar.MILLISECOND, 0);
		calendar.set(Calendar.SECOND, 0);
		calendar.set(Calendar.MINUTE, 0);
		calendar.getTimeInMillis();
	}

	/**
	 * Adjust the given calendar to the last millisecond of the specified date.
	 * 
	 * @param calendar
	 *            calendar to adjust.
	 */
	public static void endOfDay(Calendar calendar) {
		calendar.add(Calendar.DATE, 1);
		startOfDay(calendar);
		calendar.add(Calendar.MILLISECOND, -1);
	}

	/**
	 * Adjusts the given calendar to the start of the period as indicated by the
	 * given field. This delegates to startOfDay, -Week, -Month, -Year as
	 * appropriate.
	 * 
	 * @param calendar
	 * @param field
	 *            the period to adjust, allowed are Calendar.DAY_OF_MONTH,
	 *            -.MONTH, -.WEEK and YEAR and CalendarUtils.DECADE.
	 */
	public static void startOf(Calendar calendar, int field) {
		switch (field) {
			case Calendar.DAY_OF_MONTH:
				startOfDay(calendar);
				break;
			case Calendar.MONTH:
				startOfMonth(calendar);
				break;
			case Calendar.WEEK_OF_YEAR:
				startOfWeek(calendar);
				break;
			case Calendar.YEAR:
				startOfYear(calendar);
				break;
			case DECADE:
				startOfDecade(calendar);
				break;
			default:
				throw new IllegalArgumentException("unsupported field: " + field);

		}
	}

	/**
	 * Returns a boolean indicating if the calendar is set to the start of a
	 * period as defined by the given field. This delegates to startOfDay,
	 * -Week, -Month, -Year as appropriate. The calendar is unchanged.
	 * 
	 * @param calendar
	 * @param field
	 *            the period to adjust, allowed are Calendar.DAY_OF_MONTH,
	 *            -.MONTH, -.WEEK and YEAR and CalendarUtils.DECADE.
	 * @throws IllegalArgumentException
	 *             if the field is not supported.
	 */
	public static boolean isStartOf(Calendar calendar, int field) {
		switch (field) {
			case Calendar.DAY_OF_MONTH:
				return isStartOfDay(calendar);
			case Calendar.MONTH:
				return isStartOfMonth(calendar);
			case Calendar.WEEK_OF_YEAR:
				return isStartOfWeek(calendar);
			case Calendar.YEAR:
				return isStartOfYear(calendar);
			case DECADE:
				return isStartOfDecade(calendar);
			default:
				throw new IllegalArgumentException("unsupported field: " + field);
		}
	}

	/**
	 * Checks the given dates for being equal.
	 * 
	 * @param current
	 *            one of the dates to compare
	 * @param date
	 *            the otherr of the dates to compare
	 * @return true if the two given dates both are null or both are not null
	 *         and equal, false otherwise.
	 */
	public static boolean areEqual(Date current, Date date) {
		if ((date == null) && (current == null)) {
			return true;
		}
		if (date != null) {
			return date.equals(current);
		}
		return false;
	}

	/**
	 * Returns a boolean indicating whether the given Date is the same day as
	 * the day in the calendar. Calendar and date are unchanged by the check.
	 *
	 * @param today
	 *            the Calendar representing a date, must not be null.
	 * @param now
	 *            the date to compare to, must not be null
	 * @return true if the calendar and date represent the same day in the given
	 *         calendar.
	 */
	public static boolean isSameDay(Calendar today, Date now) {
		Calendar temp = (Calendar) today.clone();
		startOfDay(temp);
		Date start = temp.getTime();
		temp.setTime(now);
		startOfDay(temp);
		return start.equals(temp.getTime());
	}

	/**
	 * Returns a boolean indicating whether the given Date is in the same period
	 * as the Date in the calendar, as defined by the calendar field. Calendar
	 * and date are unchanged by the check.
	 *
	 * @param today
	 *            the Calendar representing a date, must not be null.
	 * @param now
	 *            the date to compare to, must not be null
	 * @return true if the calendar and date represent the same day in the given
	 *         calendar.
	 */
	public static boolean isSame(Calendar today, Date now, int field) {
		Calendar temp = (Calendar) today.clone();
		startOf(temp, field);
		Date start = temp.getTime();
		temp.setTime(now);
		startOf(temp, field);
		return start.equals(temp.getTime());
	}

	/**
	 * Returns a boolean to indicate whether the given calendar is flushed.
	 * <p>
	 * 
	 * The only way to guarantee a flushed state is to let client code call
	 * getTime or getTimeInMillis. See
	 * 
	 * <a href=http://forums.java.net/jive/thread.jspa?threadID=74472&tstart=0>
	 * Despairing in Calendar</a>
	 * <p>
	 * Note: this if for testing only and not entirely safe!
	 * 
	 * @param calendar
	 * @return
	 */
	public static boolean isFlushed(Calendar calendar) {
		return !calendar.toString().contains("time=?");
	}
}
